import java.util.LinkedList;
import java.util.Queue;

class Solution2 {
    public int[] dx = {0, 0, 1, -1};
    public int[] dy = {1, -1, 0, 0};
    public void solve(char[][] board) {
        int m = board.length;
        int n = board[0].length;
        for(int i = 0; i < m; i++){
            if(board[i][0] == 'O'){
                bfs(board, i, 0);
            }
            if(board[i][n - 1] == 'O'){
                bfs(board, i, n - 1);
            }
        }
        for(int i = 0; i < n; i++){
            if(board[0][i] == 'O'){
                bfs(board, 0, i);
            }
            if(board[m - 1][i] == 'O'){
                bfs(board, m - 1, i);
            }
        }
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(board[i][j] == 'P'){
                    board[i][j] = 'O';
                }else if(board[i][j] == 'O'){
                    board[i][j] = 'X';
                }
            }
        }
    }
    public void bfs(char[][] board, int i, int j){
        int m = board.length;
        int n = board[0].length;
        Queue<int[]> queue = new LinkedList<>();
        queue.offer(new int[] {i, j});
        board[i][j] = 'P';
        while(!queue.isEmpty()){
            int[] point = queue.poll();
            int a = point[0];
            int b = point[1];
            for(int k = 0; k < 4; k++){
                int x = a + dx[k];
                int y = b + dy[k];
                if(x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O'){
                    queue.offer(new int[] {x, y});
                    board[x][y] = 'P';
                }
            }
        }
    }
}
